Blasting method

ABSTRACT

Auxiliary explosive charge may be used to mix the ingredients of a shothole charge. Detonating fuse cord may thus be used to distribute fuel oil through ammonium nitrate which is loaded separately into the shothole.

United States Patent 72] inventor Gordon Alger'leichmnnn 50 11.111 orsemh 102/22-24;

Colehester, England 86/20(.5); 149/2 [21] AppLNo. 785,704 [22] Filed Dec.20, 1968 I 'RderencsClted [451' Patented Oct. 5, 1971 UNITED STATES PATENTS 1 Assign Imperial Chmkfllndwfi. Limited 3,046,889 7/1962 Merten 102/24 Lo m i 3,094,069 6/1963 Hradelet aL. 102/23 1 Pnomy Jan-1,1968 3,112,701 l2/l963 Grebe 102/22 [2 3,ll9,332 l/l964 Grebe e'tal. l02/23 I 1 Primary Examiner-Verlin R. Pendegrass H M V Attorney-CushmamDarbydzCushman [54] BLASTING METHOD 25 clams 2 P ABSTRACT: Auxiliary explosive charge may be used to mix [52] 11.5.0 102/23, the ingredients of a shothole charge. Detonating fuse cord l02/24R may thus be used to distribute fuel oil through ammonium [51] Int." "M 1/00 nitrate which is loaded separately intothe shothole.

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MMFQWMQWQ M V H nitrate BLASTING METHOD sive charge assembly for blasting and to an explosive accessm ry for use in said method and the said charge assembly.

In large-scale blasting operations it is now customary to em-- ploy relatively insensitive blasting explosives based on ammonium nitrate. These include, for example, ammonium explosives sensitized by nitroglycerine or trinitrotoluene, the so-called ANFO explosives, which are mixtures of ammonium nitrate and fuel oil, and slurried explosives which comprise ammonium nitrate and water. In order to improve the power of these compositions and their sensitivity to initiation by explosive shock wave, it is usual to incorporate therein powdered metal, for example aluminum, magnesium, iron, silicon or boron. The compositions are, however, thereby rendered less safe from premature initiation caused by accidental impact or friction or by chemical attack on the sensitizing ingredient. In order to reduce the hazard in handling of 1 the shothole with a main explosive charge, a column of powdered metal surrounding a charge of high explosive having a higher velocity of detonation than the main charge and sufficient to disperse the powdered metal and detonating both explosive charges. In the explosion, part, at least, of the powdered metal is dispersed and oxidized in the after detonation gases with consequent increase in the heat of explosion and I the gas presure.

. From one aspect invention consists in a method of blasting wherein a column of a main charge of blasting explosive, a

column of powdered metal and an auxiliary charge of explosive having a higher velocity of detonation than the main charge and sufficient to disperse the powdered metal are loaded into a shothole so that the column of powdered metal surrounds the auxiliary charge and is in contact with the main charge, and the explosive charges are detonated. The explosive charges may be detonated in known manner using, for example, end or intermediate priming or a combination of both fonns of priming.

From another aspect the invention consists in an explosive charge assembly for blasting which comprises a column of a main explosive charge, a column of powdered metal in contact with the said main charge and, disposed within the column of powdered metal, an auxiliary charge of explosive of higher velocity of detonation than the main charge and sufficient to disperse the column of powdered metal.

The invention also includes an explosive accessory for use in the blasting method and the explosive charge assembly of the invention, which comprises a packaged column of powdered metal surrounding a charge of explosive having a high velocity of detonation and capable of dispersing the powdered metal. The powdered metal is conveniently packaged in a container, for example, of synthetic plastics film such as polyethylene or polyvinyl chloride.

The beneficial effects of the invention may be achieved using any kind of blasting explosive, but the effect is most marked with relatively insensitive explosives, for example ANFO explosives and 'slurried explosives.

Preferably the main explosive charge is disposed as an annular column around the column of powdered metal and it is also preferable for the auxiliary explosive to be an elongated charge surrounded along its length by the powdered metal. The preferred arrangement is one in which the explosive charges and the column of powdered metal are coaxial.

An especially convenient auxiliary charge comprises detonating fuse cord which may also be used to prime the maincharge. If desired, additional priming charges may be attached at the end or at intermediate positions on the detonating fuse cord. A suitable fuse cord is one containing 20-100 grains of pentaerythritol tetranitrate (PETN) per foot.

A preferred method of blasting in accordance with the invention comprises disposing lengthwise in a shothole a length of detonating fuse cord surrounded along at least part of its length with a column of powdered metal contained in a thinwalled, tubular container, loading a charge of ANFO or slurried explosive around the powdered metal in theshothole and detonating the detonating fuse cord and the explosive charge.

When the detonating fuse cord is surrounded with powdered metal a further advantage which is realized is that an insensitive explosive main charge composition is protected from becoming partially desensitized by compression on detonation of an adjacent detonating fuse cord charge which is lllillfl h cient to initiate the main charge to detonation, as may happen when a length of detonating fuse cord is used to communicate detonation to a primer at the bottom of a relatively insensitive main charge at the bottom of a shothole.

The powdered metal may comprise, for example, aluminum magnesium, iron, silicon or boron. It may. conveniently be in dry powder from or in suspension in a liquid, for example water, the suspension being easier to fill into plastics tubing and giving apparently superior blasting performance when used with ANFO explosive. The suspending liquid may advantageously be thickened by dissolving therein a thickener, for example guar gum, ground psyllium seed or water-soluble cellulose ether.

The preferred metal powder is granular aluminum of particle size such that substantially all passes a 8.8. l0 mesh-sieve and at least 50 percent is retained on a 8.8. 30-mesh sieve.

In order to further illustrate the invention a preferred method of blasting is hereinafter particularly described, by way of example only, with reference to the accompanying drawings wherein FIG. 1 shows diagrammatically a sectional elevation of an explosive charge assembly loaded in a vertical shothole;

FIG. 2, shows a cross section of the loaded shothole on the line "-11 of FIG. 1.

The shothole 10 contains a priming charge of high explosive l l at the bottom and a centrally disposed explosive accessory charge, consisting of a length of commercial detonating fuse cord 12 (Cordtex -Registered Trade Mark) and a surrounding layer of powdered metal 13 contained in a polythene tube 14. One end of the cord 12 is attached to the charge II and the other end extends beyond the top of the shothole and has attached to it a detonator 15 by which it may be initiated. A main charge 16 of powdered explosive is loaded by pouring it around the polythene tube 14 and is covered by stemming 17.

when the detonator 15 is fired the fuse cord 12, the priming charge 11 and the main charge 16 are detonated and the powdered metal 13 is dispersed and oxidized in the gases formed in the detonation.

The following examples further illustrate the practice of the invention. In the examples all parts and percentages quoted are by weight.

EXAMPLE I Ten blasting explosive charges were tired in a limestone quarry bench blast in shotholes 4 pounds Inches in dhlneter and 60 feet deep, spaced at l2-feet intervals with a burden of 12 feet. Five adjacent holes at one side of the bench were loaded in accordance with the invention, as illustrated. The priming charge II in each shothole was a 40 pounds base charge of a nitroglycerine gelatinous explosive sold commercially by Imperial Chemical Industries Llmited as Togel' (Registered Trade Mark) which filled the bottom 10 feet of the shothole. The detonating fuse cord 12 was Cordtex fuse cord containing 50 grains of PETN per foot. The powdered material 13 was granular aluminum powder, of particle size such that substantially all passed a 8.8. l6-mesh sieve and 60 percent was retained on a BS. 30-mesh sieve, contained in a %-inch diameter polythene tube at a loading density of 0.23 pound/foot. The main charge 16 was pounds of an ANFO mixture consisting of 94 percent ammonium nitrate and 6 percent of diesel oil, which was poured around the Togel and the aluminum charge 13, filling the shothole to a height of 30 feet The shothole was stemmed with quarry grit stemming 17 to the top. The remaining five adjacent holes were similarly charged except that'the aluminum powder charge 13 and the detonating fuse cord 12 were omitted and the priming charge was fired by an electric detonator.

When the blast was fired the blasting charges in the first five I shotholes gave better rock fragmentation and rock throw than was obtained from the charges in the second five holes.

EXAMPLE 2 Ten blasting charges were prepared and fired by the method of the invention in the same manner as described for the first five shotholes in example I, except that the main charge 16 was a charge of slurried composition consisting of 87 percent ammonium nitrate, l2 percent of water and 1 percent of guar gum, which was not sufficiently sensitive to propagate detonation in a 4-inch diameter shothole.

The blast gave better rock fragmentation and rock throw than was obtained from a similar blast from which the aluminum powder was omitted.

EXAMPLE 3 In this example the detonating fuse cord 12 (Cordtex) Cordtex) and the surrounding column of aluminum powder 13 were the same as those used in example 1 except that they were assembled from smaller units. Each unit consisted of a 6- foot length of Cordtex' surrounded by a 4% foot length of aluminum powder contained in polythene tubing 14 which was sealed by tying the ends tightly around the CordtexCordtex fuse cord Twelve units were joined together by tying the bare end portions of the Cordtex fuse cord together and covering the knots with adhesive tape.

In the blast of this example, l charges were fired in a quarry bench blast in shotholes 4 inches in diameter and 70 feet deep, spaced at 15 feet intervals with a burden of l 1 feet. The holes were loaded as illustrated in the accompanying drawings, the priming charge being a l0 pound cartridge of Togel explosive. The assembled units of aluminum powder and 'Cordtex fuse cord extended 60 feet from the bottom of the hole and a further length of Cordtex fuse cord attached to the fuse cord of the uppennost unit was led from the top of each shothole. The main charge 16 was 240 pound of an ANFO mixture as used in example 1. The top 10 feet of each shothole were stemmed with quarry grit stemming 17.

When the explosive charges were fired the blasting results were excellent. The fragmentation was superior to that ohtainable when the aluminum powder was omitted and was comparable to that obtainable using shotholes spaced at 10 feet with a burden of 10 feet without using the aluminum powder.

EXAMPLE 4 with a spacing of 10 feet and a burden of 10 feet. Seven adv jacent holes at one side of the bench were loaded in accordance with the invention as illustrated in the accompanying drawing. The primer 1] in each shothole was a 10 pound cartridge of 'Togel' explosive and the main charge 16 in each shothole was 120 pound of ANFO explosive as used in example l, which filled the shothole to a depth of 33 feet. The remaining 8 feet of each shothole were filled with quarry grit stemming 17. The remaining 7 shotholes were charged in the same manner except that the aluminum powder 13 was omitted.

When the blast was fired the fragmentation and rock throw were better on the side of the bench where the aluminum powder was used than on the other side.

EXAMPLE 5 The blast of example I was repeated except that the column of aluminum powder 13 in each shothole loaded in accordance with the invention was in the form of an extrudable aqueous suspension consisting of 40 parts of aluminum suspended in 60 parts of water containing 2 percent of guar gum. I

When the blast was fired, better fragmentation and rock throw were obtained from the charges which were loaded into aluminum shotholes in accordance with the invention than from those from which the aluminum was omitted. EXAM- PLE EXAMPLE 6 The blast of example 1 was repeated except that powdered magnesium was used instead of the powdered aluminum. The results obtained were the same as those obtained in example I.

EXAMPLE 7 The blast of example 1 was repeated except that powdered silicon was charge instead of powdered aluminum. The results obtained were the same as those obtained in example I.

What we claim is:

l. A method of blasting comprising: loading into a shothole a column of a main charge of blasting explosive, a column of powdered metal and an auxiliary charge of explosive having a higher velocity of detonation than the main charge, the auxiliary charge being surrounded by the column of powdered metal and being in sufficient amount to disperse at least part of the powdered metal in the after-detonation gases of the main charge; and detonating the charges.

2. A method as claimed in claim 1 wherein the main charge of blasting explosive is selected from the group consisting of an ANFO explosive and a slurried explosive.

3. A method as claimed in claim 1 wherein the main charge of blasting explosive is dispersed as an annular column around the powdered metal or metalloid.

4. A method as claimed in claim 1 wherein the auxiliary explosive charge is an elongated explosive charge.

5. A method as claimed in claim 1 wherein the auxiliary charge comprises a detonating fuse cord.

6. A method as claimed in claim 1 wherein the explosive charges and the column of powdered metal are disposed coaxially in the shothole.

7. A method as claimed in claim 1 wherein the powdered metal is selected from the group consisting of powdered aluminum magnesium, iron, silicon and boron.

8. A method as claimed in claim 1 which comprises disposing lengthwise in a shothole a length of detonating fuse cord surrounded along at least part of its length with a column of powdered metal contained in a thin-walled container, loading a charge selected from the group consisting of ANFO and slurried explosive around the powdered metal in the shothole and detonating the detonating fuse cord and the explosive charge.

9. A method as claimed in claim 1 wherein the column of powdered metal is contained in tubular plastics film.

10. A method as claimed in claim 9 wherein the plastics film is selected from the group consisting of polyethylene and polyvinyl chloride.

11. An explosive charge comprising a column of a main charge of blasting explosive, a column of powdered metal and, surrounded by the column of powdered metal, an auxiliary charge of explosive of higher velocity of detonation than the main charge and in sufficient amount to disperse at least part of the column of powdered metal in the after-detonation gases of the main charge.

12. An explosive charge assembly as claimed in claim 11 wherein the powdered metal is selected from the group consisting of aluminum, magnesium, iron, silicon and boron.

13. An explosive charge assembly as claimed in claim 11 wherein the powdered metal or metalloid is contained in a thin-walled tubular container.

14. An explosive charge assembly as claimed in claim 13 wherein the said container is tubular plastics film.

15. An explosive charge assembly as claimed in claim 14 wherein the platic is selected from the group consisting of polyethylene and polyvinyl chloride.

16. An explosive charge as claimed wherein the auxiliary explosive charge is an elongated charge.

17. An explosive charge as claimed in claim 16 wherein the auxiliary explosive charge comprises detonating fuse cord.

18. An explosive charge as claimed in claim 11 wherein the main explosive charge is selected from the group consisting of ANFO and slurried blasting explosive.

19. An explosive charge assembly as claimed in claim 11 wherein the main explosive charge is disposed as an annular column around the powdered metal,

20. An explosive charge assembly as claimed in claim l9 wherein the explosive charges and the powdered metal are coaxial.

21. An explosive accessory for use in blasting comprising a column of powdered metal packed in a container and, surrounded by said column, a charge of explosive having a higher velocity of detonation than ANFO and in sufficient amount to disperse at least part of the powdered metal in the afterdetonation gases of an explosive charge detonated in contact with the accessory.

22. An explosive accessory as claimed in claim 21 wherein the powdered metal is packaged in a container of synthetic plastics film.

23. An explosive accessory as claimed in claim 22 wherein the plastic is selected from the group consisting of polyethylene and polyvinyl chloride.

24. An explosive accessory as claimed in claim 28 wherein the explosive charge comprises detonating fuse cord.

25. An explosive accessory as claimed in claim 28 wherein the powdered metal is selected from the group consisting of aluminum magnesium, iron, silicon, and boron. 

1. A method of blasting comprising: loading into a shothole a column of a main charge of blasting explosive, a column of powdered metal and an auxiliary charge of explosive having a higher velocity of detonation than the main charge, the auxiliary charge being surrounded by the column of powdered metal and being in sufficient amount to disperse at least part of the powdered metal in the after-detonation gases of the main charge; and detonating the charges.
 2. A method as claimed in claim 1 wherein the main charge of blasting explosive is selected from the group consisting of an ANFO explosive and a slurried explosive.
 3. A method as claimed in claim 1 wherein the main charge of blasting explosive is dispersed as an annular column around the powdered metal or metalloid.
 4. A method as claimed in claim 1 wherein the auxiliary explosive charge is an elongated explosive charge.
 5. A method as claimed in claim 1 wherein the auxiliary charge comprises a detonating fuse cord.
 6. A method as claimed in claim 1 wherein the explosive charges and the column of powdered metal are disposed coaxially in the shothole.
 7. A method as claimed in claim 1 wherein the powdered metal is selected from the group consisting of powdered aluminum magnesium, iron, silicon and boron.
 8. A method as claimed in claim 1 which comprises disposing lengthwise in a shothole a length of detonating fuse cord surrounded aloNg at least part of its length with a column of powdered metal contained in a thin-walled container, loading a charge selected from the group consisting of ANFO and slurried explosive around the powdered metal in the shothole and detonating the detonating fuse cord and the explosive charge.
 9. A method as claimed in claim 1 wherein the column of powdered metal is contained in tubular plastics film.
 10. A method as claimed in claim 9 wherein the plastics film is selected from the group consisting of polyethylene and polyvinyl chloride.
 11. An explosive charge comprising a column of a main charge of blasting explosive, a column of powdered metal and, surrounded by the column of powdered metal, an auxiliary charge of explosive of higher velocity of detonation than the main charge and in sufficient amount to disperse at least part of the column of powdered metal in the after-detonation gases of the main charge.
 12. An explosive charge assembly as claimed in claim 11 wherein the powdered metal is selected from the group consisting of aluminum, magnesium, iron, silicon and boron.
 13. An explosive charge assembly as claimed in claim 11 wherein the powdered metal or metalloid is contained in a thin-walled tubular container.
 14. An explosive charge assembly as claimed in claim 13 wherein the said container is tubular plastics film.
 15. An explosive charge assembly as claimed in claim 14 wherein the plastic is selected from the group consisting of polyethylene and polyvinyl chloride.
 16. An explosive charge as claimed wherein the auxiliary explosive charge is an elongated charge.
 17. An explosive charge as claimed in claim 16 wherein the auxiliary explosive charge comprises detonating fuse cord.
 18. An explosive charge as claimed in claim 11 wherein the main explosive charge is selected from the group consisting of ANFO and slurried blasting explosive.
 19. An explosive charge assembly as claimed in claim 11 wherein the main explosive charge is disposed as an annular column around the powdered metal,
 20. An explosive charge assembly as claimed in claim 19 wherein the explosive charges and the powdered metal are coaxial.
 21. An explosive accessory for use in blasting comprising a column of powdered metal packed in a container and, surrounded by said column, a charge of explosive having a higher velocity of detonation than ANFO and in sufficient amount to disperse at least part of the powdered metal in the after-detonation gases of an explosive charge detonated in contact with the accessory.
 22. An explosive accessory as claimed in claim 21 wherein the powdered metal is packaged in a container of synthetic plastics film.
 23. An explosive accessory as claimed in claim 22 wherein the plastic is selected from the group consisting of polyethylene and polyvinyl chloride.
 24. An explosive accessory as claimed in claim 28 wherein the explosive charge comprises detonating fuse cord.
 25. An explosive accessory as claimed in claim 28 wherein the powdered metal is selected from the group consisting of aluminum magnesium, iron, silicon, and boron. 